Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/40—Making wire or rods for soldering or welding
  • B23K35/402—Non-consumable electrodes; C-electrodes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
  • B23K20/22—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating taking account of the properties of the materials to be welded
  • B23K20/233—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating taking account of the properties of the materials to be welded without ferrous layer
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49002—Electrical device making

Definitions

• the present invention relates to methods of manufacturing electrodes for metal-working with an electric arc and, more particularly, is related to methods of manufacturing nonconsumable copper-zirconium electrodes.
• the invention can be used for manufacturing bi-metal articles of a considerable length, wherein the external diameter is 5 to 15 times as great as the diameter of the core, the jointed metals having different structures and displaying different plastic properties when worked by the application of pressure.
• the present invention can be utilized to the utmost effectiveness in the manufacture of electrodes for air-plasma cutters, including a sleeve and a zirconium core.
• Copper is usually taken as the sleeve material, owing to its high heat and electric conductivity.
• the material of the core there is usually taken either pure zirconium or one of its alloys with a small content of the alloyed metal, e.g. such alloys as Zr + 1% Nb.
• the sleeve and the zirconium core are prepared separately. Then the copper core is pressure-fitted into the blind bore of the sleeve without heating.
• the joint thus obtained fails to provide a reliable thermal and electric contact as there are gaps and clearances left between the two components, particularly, at the area of the end face of the core.
• the technological process is a labor-consuming one, which is particularly true of the operations connected with centering the core, with any mechanisation and automation of the production process being complicated, considering that the process involves producing the relatively short less than 4 mm) core by turning and accurately locating it in the sleeve. Therefore, the electrodes produced by the abovedescribed known technique have a service life which is insufficient for their industrial application, which has been reflected in the fact that plasmatrons with air stabilization of the arc have not been yet developed to the degree to which they are capable.
• a known improvement of the abovedescribed technology is making entire electrodes of a bi-metal copper-zirconium blank, by drilling a bore in a massive sleeve and then fitting into this bore the zirconium core, while applying a relatively low pressure.
• the blank thus obtained is subjected to hot deformation and then cold-drawn to the final dimensions, whereafter electrodes are produced therefrom by turning the blanks in automatic lathes.
• the large-sized sleeve is produced either by casting or by hot molding.
• copper produced by said methods has a non-uniform macro-crystalline structure, whereby the plastic properties of a blank made of such copper vary to a considerable degree at various areas of the blank.
• the copper-zirconium blank is subjected to joint hot deformation, on account of the exhibition of the Theological properties of different metals (copper and zirconium) during their joint plastic flow there often takes place an unpermissible distortion of the core, viz. its cross-sectional area varies along the length of the blank and its shape in cross-section becomes either cross-like or, at the best, rectangular.
• a third metal is taken as the material of the intermediate layer. Said latter acting as an interface, of for example, during the hot deformation the metals of the core and of the sleeve form a low-melting eutectic, or else the intermediate layer acts as a solder. Thin intermediate layers are used, e.g. made of a foil or of a band. As a result of the subsequent deformation, the intermediate layer thins out and becomes accommodated between the metals being joined as a very thin interface, following the crystalline structure of the surface of the joint. Said known method is used when the ratio of the diameter of the sleeve to the diameter of the core is substantially less than 5:1.
• the crystalline structure of the joint area becomes exhibited so considerably that the cross-section on the core acquires an irregular shape, and the variation of the cross-sectional area of the core along the length of a blank becomes as high as 50% of the rated value, the interface, of which the thickness in the deformed blank is but one tenth and less of the width of the serrated borderline between the core and the sleeve, failing to serve as the interface levelling out this borderline.
• electrodes made of this blank have inadequately long service life, with the plasma jet being insufficiently stable, and the crater developed in the core likewise having an irregular shape.
• the blanks for electrodes are subjected to machining either in turret lathes or by stamping. However, it is impossible to produce qualitative cathodes from the blanks according to the known method.
• the intermediate layer is of a thickness substantially equal to the diameter of the core and is made of cold-deformed copper, the deformation of the blank being effected consecutively by, first, cold deformation of the intermediate layer on the core and, then, their hot deformation jointly with the sleeve.
• the intermediate layer having a thickness substantially equalling the diameter of the core, it becomes possible to attain a cross-sectional shape of the core which for every practical reason does not differ from a circle.
• This substantial equality of the thickness of the intermediate layer and the diameter of the core is aimed at levelling out the conditions of the mutual influence of the structures of zirconium and copper upon the formation of their contact zone or interface, as well as at completely eliminating the influence of the macro-crystalline structure of the copper sleeve upon this contact area.
• An additional advantage of the use of the intermediate layer is that the bore which is to be drilled in the massive copper sleeve is three times as great as the one that is to be drilled when no intermediate layer is used. Furthermore, it is no longer necessary to ensure the high accuracy and fine finish of the internal surface of the bore, since with the intermediate layer interposed, these factors do not influence at all the formation of the contact area and the shape of the core. Moreover, the copper sleeve forms a quality joint with the intermediate layer during hot deformation even when the surfaces are not specifically prepared in advance. With copper used as the intermediate layer, a high thermal and electric conductivity of an electrode is provided, while the cold-deformed structure of the copper of the intermediate layer is responsible for the finely crystalline structure of the surface of the contact.
• the heating prior to the hot deformation should be of a short duration, e.g. induction heating.
• the width of the contact area (the "serration") in the zirconiumcopper bi-metal is minimized and practically does not affect the cross-sectional shape of the core, which shape does not practically differ from a circle in the hot-deformed blank.
• the deformation of the blank is effected in successive steps.
• the joint cold deformation of the intermediate layer on the core owing to the high compression forces characteristic of the cold deformation technique, ensures snug, pre-strained, clearance-free connection of the zirconium and copper bodies and retains the cold-deformed structure of the metal of the intermediate layer.
• this clearance-free connection prevents oxidation of the surface of the core, experience showing that merely slight oxidation can be detected following the heating exclusively adjacent to the end face, to a 5 to 10 face, to a 5 to 10 mm distance from the face.
• the hot deformation should be effected by compression at a temperature of about 650° C to 750° C with subsequent drawing of the blank to a degree of deformation within 15% to 40%, to a diameter substantially equal to the diameter of the electrode to be manufactured.
• the high compressing effort brought about by the compression provides for reliable joining of the layers of the bimetal blank, and the concentricity of the cross-sections is retained, like at cold drawing.
• the strength and plastic properties of zirconium, particularly those of alloys of zirconium with a small amount of the alloying elements, are considerably different from those of copper at room temperatures.
• the upper temperature limit is due to the fact that at a higher temperature under the hot compression conditions zirconium and cold-deformd copper undergo recrystallization.
• the distortion of the cross-sectional shape of the core is increased to a degree that cannot be tolerated, because the width of the serrated zone of the joint depends predominantly on the size of the grains of the metals being joined.
• the serrated zone of the joint is meant the maximum difference between the respective radii of the peaks and valleys of the contact surfaces of the layer and the core.
• Still another limitation of the temperature of the range is the fact that at the temperature of 862° C copper and zirconium form a low-melting eutectic.
• the safety margin in the case of temperatures of this kind is preferably about 100° C, so that the high pressures and heat generated by the deformation themselves would not lead to the formation of the eutectic at lower temperatures.
• the bottom temperature limit is explained by the increased non-uniformity of the deformation on account of the difference between the strength and plastic properties of copper and zirconium increasing with the temperature decrease, as well as by the known phenomenon of the quality of the joining of layers of different metals becoming poorer at lower temperatures and by the necessity of using presses with extra-high effort value, when a temperature is low.
• the subsequent drawing of a compressed blank be carried out with the degree of deformation within 15% to 40%, to a diameter substantially equal to that of the electrode to be made.
• the lower limit of this deformation range is explained by the necessity of attaining a uniform colddeformed structure of the entire cross-section of the blank. It is known that hot-deformed copper is too soft and poorly machined, whereas cold-deformed copper is stronger and can be machined to better results. Further, there is required a certain degree of deformation by drawing to straighten out the compressed blank, to reduce the diameter tolerance down to 0.1 - 0.2 mm and to obtain a surface finish not poorer than Class 7.
• the extension strain which is at its maximum adjacent to the axis of the blank results in the core displaying a tendency to break and to form throat portions, as if being extended.
• the ratio of the diameter of the copper sleeve to the diameter of the core is preferably within the range of about 5 to 15.
• Disclosure is made of a method of manufacturing a nonconsumable copper-zirconium electrode, according to which a zirconium core is placed within a thick-wall copper sleeve, with an intermediate layer disposed between the sleeve and the core.
• the assembled three-component blank is deformed and then machined.
• the intermediate layer is of a thickness substantially equal to the diameter of the core, to level out the conditions of the inter-influence of the structures of the copper and zirconium bodies upon the formation of the contact zone, and also to preclude the influence of the macrocrystalline structure of the copper sleeve upon this contact zone.
• the deformation of the blank is carried out in successive stages.
• the joint cold deformation of the intermediate layer on the zirconium core provides for the pre-strained clearance-free joining of the copper and zirconium and for the retaining of the cold-deformed structure of the intermediate layer.
• the pre-strained joining retains during the subsequent heating of the blank an adequately sealed away state of the zirconium core, not-withstanding the fact that the thermal expansion factor of copper is more than twice that of zirconium.
• the cold-deformed copper-zirconium blanks are then cut to lengths to be placed inside thick-wall copper sleeves by fitting under a slight pressure.
• the subsequent hot deformation provides for a tight metal bond of the core with the intermediate layer and of the latter with the sleeve.
• the cold deformation of the intermediate layer on the core is carried out according to the presently described embodiment of the method by drawing to a degree of deformation sufficient for obtaining the clearance-free pre-strained joint.
• the subsequent hot deformation of the assembled threecomponent blank is carried out at a temperature form 650° C to 750° C, with consecutive drawing of the blank with a degree of deformation within 15% to 40%, to a diameter substantially equal to that of the electrode to be made.
• the thus produced elongated blanks have a fine surface finish and an adequate concentricity of the core, which enables the manufacture of electrodes from a continuous blank having an external diameter 5 to 15 times as great as the diameter of the core.
• a blank of hot-pressed copper 87 mm in diameter and 150 mm long is taken, and a 20 mm diameter bore is drilled therein in an automatic lathe.
• the latter is turned to a 84 mm diameter.
• Zirconium cores 6.8 mm in diameter are located in this tube, and the assembly is cold-drawn in a single pass to a 20 mm external diameter.
• the clearance-free joint is produced by this drawing, owing to the upsetting of the copper tube from the 24 mm diameter to the 20 mm one and to the wall thinning from 7.5 mm to 7.1 mm.
• a three-component blank thus obtained is induction-heated to 700° C and then compressed into a blank 15 mm in diameter.
• the hot-pressed blanks are pickled, whereafter they are drawn in a drawing mill with a 30% degree of deformation to a 12.5 mm diameter, the zirconium core thinning down to a 1.0 mm diameter.
• the pulling end portion is then cut off the blank; the latter is trued in a trueing machine, whereafter electrodes are made therefrom by turning in turret lathes.
• electrodes are manufactured having a long life of service for plasma-cutting of various metals and alloys.
• the microstructural analysis of the bond between the copper and zirconium has indicated the presence of a metallurgincal bond.
• the cross-section shape of the core practically does not differ from a circle, and the joint between the copper and zirconium bodies is effected along a highly developed finelycrystalline surface, which becomes obvious when the core is exposed by etching away the copper. Owing to the high-quality bond between the copper and zirconium and to the accurate concentricity of the core in the sleeve, there is attained a stable plasma arc with uniform burning away of the zirconium core.
• the number of actuations without electrode replacement becomes above 400 to 500, at a nominal thermal load of the cutter.
• the production of electrodes by the disclosed method is readily susceptible to mechanisation and automation and can be performed by commonly available equipment.
• the amount of labor consumed during the manufacture of electrodes by the herein disclosed method is less than one third of that of the previously existing manufacturing technique.
• the herein disclosed method provides for setting up a large-series production of electrodes for air-plasma cutters.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Wire Bonding (AREA)
• Arc Welding In General (AREA)
• Discharge Heating (AREA)

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• 1975
  • 1975-03-10 SU SU7502119847A patent/SU568475A1/ru active
• 1976
  • 1976-03-05 US US05/664,072 patent/US4018375A/en not_active Expired - Lifetime
  • 1976-03-05 GB GB8853/76A patent/GB1523659A/en not_active Expired
  • 1976-03-09 FR FR7606710A patent/FR2303634A1/fr active Granted
  • 1976-03-09 SE SE7603130A patent/SE412181B/sv unknown
  • 1976-03-10 DE DE2610009A patent/DE2610009C3/de not_active Expired

Patent Citations (4)

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